Abstract
Ultra-relativistic heavy ion collisions facilitate the creation of high temperature and pressure that is sufficient to produce the Quark Gluon Plasma (QGP), which is a deconfined state of matter where quarks and gluons interact with each other. At the Large Hadron Collider (LHC), lead ions are accelerated to an energy
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of 1.38 TeV per nucleon. The collisions of lead-lead ions is expected to produce the QGP for a very short interval of time (10 fm/c), which is studied using various experimental probes. These probes can be investigated using the ALICE detector at the LHC. Heavy quarks (charm and beauty) are of particular interest as they are predominantly produced in the early stage of the collisions by hard scattering processes before the formation of the QGP due to their large mass. They traverse through the medium undergoing interactions and experience the full evolution of the system. Heavy quarks eventually fragment to form heavy flavor hadrons. Thus studying heavy flavor hadrons provide information about the properties of the QGP. One way to study heavy flavor hadrons is by measuring the electrons via their semi-leptonic decay channels (heavy-flavor decay electron). Heavy ion collisions are studied by measuring various experimental observables, such as the nuclear modification factor and the azimuthal anisotropy of particles produced in the event. The dynamics of parton (quarks and gluons) interaction with the QGP can be studied via two particle azimuthal angular correlations. This involves measuring the distribution of relative azimuthal angles, Δϕ, between a trigger particle and an associated particle. The correlations at Δϕ ~ 0 is dominated by the near-side jet, where the trigger and associated particle originate from a fragmenting parton. The correlations at Δϕ ~ π is due to the recoil or away-side jet. In this thesis, the azimuthal angular correlations of heavy-flavour decay electrons and charged hadrons are studied in pp and Pb-Pb collisions to gain more insight into the interactions of heavy quark with the QGP using the ALICE detector. In pp collisions, the Δϕ correlation is used to disentangle the contribution of charm and beauty hadrons in the heavy-flavour decay electron sample. The measurement of relative fraction of beauty decays to heavy-flavour decay electron sample is obtained for pp collisions at √s = 2.76 and 7 TeV. The cross-section of beauty decays to electrons is also obtained using the heavy-flavor decay electron cross-section in 2.76 TeV pp collisions. These measurements are compared to various perturbative Quantum Chromodynamic calculations. Due to the large mass, it is possible that heavy quarks hadronize while traversing the QGP. This could change the fragmentation function of heavy quarks. In Pb-Pb collisions, the near-side correlation distribution is studied to check any possible modification of fragmentation function of heavy quarks. The near-side yield is measured in two collision centralities, 0-8% and 20-50%, and compared with pp collisions at 7 TeV. To quantify the modification, the ratio of near-side yield of Pb-Pb to pp collisions, IAA, is obtained.
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